This invention relates to an optical system utilizing a cyclic optical imaging member. One such cyclic optical imaging member, sometimes referred to as a "ruticon", is a laminated device, characterized by elastomer and photoconductive layers. In most such cyclic imaging members, the elastomer and photo-conductive layers are sandwiched between two electrically conductive layers across which an electric field is maintained. Cyclic optical imaging members of the type described are explained in greater detail in U.S. Pat. No. 3,716,359 issued to Nicholas K. Sheridan on Feb. 13, 1973, and assigned to the same assignee.
Cyclic optical imaging members are primarily used to transfer information from an optical source to a recording or a display device. In operation, a surface of the imaging member deforms in response to light which is incident upon one of the surfaces of the imaging member. This deformation is accomplished as follows: When the photoconductor is exposed to an optical pattern, the electric field maintained across the photoconductor induces a flow of charge in those regions of the photoconductor which are exposed to the light. The flow of charge varies the electric field, creating a mechanical force which causes the elastomer to deform. The equilibrium point of the deformation occurs when the mechanical force of the electric field is balanced by the surface tension and the elastic forces of the elastomer.
Deformation may be temporary or permanent depending upon the elastic modulus of the elastomer and the magnitude of the electric field across the elastomer. For instance, permanent deformation may occur when the degree of deformation exceeds the elastic limits of the elastomer. Also, at least two types of temporary surface deformation can be observed. First, when a large electric field and a very complient elastomer are used, the elastomer will remain deformed as long as the electric field is maintained in spite of any subsequent illumination of the photoconductor. The deformation can be erased only by removing or reversing the electric field across the elastomer, allowing it to relax. The second form of temporary deformation occurs when the combination of the factors of elastic modulus of the elastomer and magnitude of the electric field are below a threshold value. In that case, the surface deformation is erased either by removing or reversing the power supply for the electric field, or by flooding the photo-conductive layer with light to erase the modulated electric field pattern.
The elastic modulus of the elastomer and the magnitude of the electric field also control the rapidity with which the deformation can be erased. Most imaging members are designed so that the elastomer springs back to its original position substantially immediately upon removal of the electric field, or upon flooding the photo-conductive layer with light. The rate of spring back is often described by an imaging member storage time, typically defined as the time for the intensity of a projected image to fall from maximum to one-half maximum.
The tendency of the imaging member to spring back substantially immediately is undesirable in many applications, such as xerography, in which a cyclic imaging member is often used as a buffer between a source of information generated at irregular time intervals and a means for recording information at regular time intervals. For instance, many cathode ray tube display devices operated by analog or digital computers provide information in varying time intervals. However, the devices used to optically record the information from the cathode ray tubes have fixed, regular cycle times. The effectiveness of the imaging member as a buffer depends upon its ability to response to varying rates of information input, and to retain the image long enough for the recording device to adequately capture the information. Most imaging members do not operate effectively as buffers, and this deficiency is not always corrected by using several imaging members in parallel, with one member acting as a storage buffer for previously encoded information, while the other is receiving date from the cathode ray tube.